Cat Genomic Resources – Karyotypes

A variety of genetic and genomic resources have been developed for the domestic cat. Each resources has added to the knowledge of the cat genome, aiding researchers in the development of the domestic cat as a model for human disease, improving the health of the feline itself, and also assisting forensic applications. All appropriate resources are welcome to be listed on this website – please submit addition resources that are novel or may have been overlooked.

Domestic Cat Karyotype

The domestic cat chromosomal complement is 2N = 38 (N = 19) with 18 autosomes and the XY sex chromosomes (XX is female, XY is male). Various cytogenetic techniques, such as R-, RBG-banding and fragile site studies, have also helped distinguish and characterize the cat chromosomes.47-49,52 For example, cats do not have a significant fragile X site on the X chromosome that is found in humans and is associated with mental retardation. Although a sequential numbering of the chromosomes has been suggested (Cho et al., 1997)3. This historical classification of chromosomes into morphologic groups has been retained in the cat.the classical chromosomal nomenclature that represents chromosomes by size and telomeric positions is still widely used to represent the cat karyotype and ideograms. Hence cats have three large metacentric chromosomes (A1 to A3), four large subtelomeric chromosomes (B1 to B4), two medium-size metacentrics (C1 to C2), four small subtelomerics (D1 to D4), three small metacentrics (E1 to E3), and two small acrocentrics (F1 and F2). The X chromosome is midsize and subtelomeric, similar to chromosome B4. All of Felidae have a similar karyotype to the domestic cat and the cat karyotype is highly representative of most carnivores.

Early chromosome staining recognized some major alterations in the felid genome, particularly the Robertsonian translocation of F1 and F2 to form chromosome C3 in the ocelot lineage of cats from South America (2N = 36)59. Minor pericentric inversions, additions, or deletions of the small chromosomes cause variation in the felid karyotype; however, overall, domestic cats have a chromosomal architecture that is highly representative for all felids and ancestral for most carnivores. 34,44 The pericentric inversion of chromosome F1 produces a small, more centromeric chromosome and represents as E4 in many cat species.

Historically, the first genetic consideration to explain reduced fertility or intersex cats is chromosomal differences, especially the loss of one of the sex chromosomes. Karyotypic and now gene-based assays are common methods to determine if a cat with ambiguous genitalia50 or a poor reproductive history has a chromosomal abnormality. Karyotypic studies of male tortoiseshell cats have shown that they are often mosaics, or chimeras, being XX/XY in all or some tissues.* The minor chromosomal differences that are cytogenetically detectable between a domestic cat and an Asian leopard cat are likely the cause of fertility problems in the Bengal cat breed, which is a hybrid between these two species. Other significant chromosomal abnormalities causing common “syndromes” are not well documented in the cat. *References 2, 4, 7, 10, 14, 19, 20, 42, 54.

Domestic Cat Chromosome Painting

The sufficient variation of cat chromosomal sizes also allowed for the easy flow sorting of cat chromosomes.56 Chromosome painting has indicated that the cat genome organization is highly conserved to that of human chromosomes. For example, the p arm of human chromosome 1(1p) is largely composed of the same genes that are on the cat chromosome defined as C1, whereas human chromosome 1q is composed of genes that are found on cat chromosome F1. The chromosome painting technique has also be performed reciprocally, implying painting cat chromosomes onto human mitotic chromosome spreads and human chromosomes onto cat mitotic chromosome spreads, revealing the high conservation of chromosomal arrangement of cat to humans,56,61 specifically compared to mice.53 Thus chromosome painting is an excellent overview of cat genome organization, 38 which greatly facilitates candidate gene approaches because the location of particular genes could be anticipated in cats from comparison with the genetic map of humans.55 This additional confirmation of conservation to human, with regard to genome organization, further supported additional genetic resource development for the cat as a valuable animal model for human disease.